Heretofore, it has required a complicated series of processes and various kinds of machines and devices for effecting such processes as to produce the aforementioned sintered base boards for electronic parts and assemblies. And, in such a series of processes, it has required a very long time and consumption of a large amount of energy for the treatment to secure desired characteristics in the products. And, moreover, very poor yield rates of products against raw powder materials could not be avoided.
As is well known, there are a dry method and wet method in the production of above-noted sintered base boards. According to said dry method, a binding agent is added in raw powder at a rate of 0.3 to 2% and granulated by a spray drying process or the like. Granules of powder thus obtained are sintered by heating at a high temperature and for a long time. A sintered block is then sliced into thin plates with a diamond cutter and such thin plates are ground finally to yield products.
And, according to the above-noted wet method, a binding agent is added in the raw powder at a high rate of 10 to 25% and kneaded in a mechanical kneader for about 50 hours so as to obtain a uniform phase of admixture. After the kneading operation, the admixture is submitted to heating for about 100 hours at a comparatively low temperature of about 300.degree. C. so that evaporation of the binding agent may be completed. After this, the dry material is sintered for about 30 hours to obtain a sintered block. Then, the sintered block is sliced into thin plates and ground as stated above.
Thus, according to each one of the known methods as stated above, such base boards cannot be produced without effecting a complicated series of treatment which requires prudent operations and consumption of a large amount of energy, and without a long processing period. Moreover, according to such known methods, loss of raw powder amounts generally to over 50%. This loss is caused mainly in the course of slicing, cutting, and grinding operations which cannot be eliminated in such known methods.
On the other hand, it has been well known that solid ceramic plates of predetermined shape and size can be produced from ceramic powder by means of a known powder molding press such as a tabletting machine. However, upon such a solid ceramic plate being heated at a high temperature, it is necessarily highly deformed. So, such a ceramic plate which has been molded by means of a known powder molding press is not available for sintering treatment which is required for the production of the aforementioned base boards for electronic parts and assemblies. It is considered that the above-noted deformation of a molded ceramic plate is caused by lack of uniformity of density in the molded body, and such lack of uniformity of density is caused primarily by lack of uniformity of powder particles which have been fed into the mold recess.
This invention therefore is directed to provide pressure molding means by means of which, molded ceramic plates having a uniform density in all portions of the molded body can be obtained to overcome the foregoing drawbacks in the old methods for the production of such base boards for electronic parts and assemblies.